Application of plasma etching techniques to metal-oxide-semiconductor (MOS) processing

Abstract

Compared with wet etching techniques for the fabrication of MOS integrated circuit (IC) devices, plasma etching can offer better line fidelity (through reduced undercutting of the resist mask), greater tolerance towards adhesion of the resist layer and, in some cases, process simplification. However, because of the small but finite etch rates of the masking resist and the substrate material, careful consideration must be given to the minimum thickness of resist used and to the maximum amount of over-etching that can be tolerated. These factors are illustrated by considering the etching of silicon nitride, aluminium and silicon dioxide layers. It is shown that the plasma etching of silicon nitride can result in process simplification, whilst the plasma etching of aluminium and aluminium-silicon layers gives excellent edge definition and is fully compatible with conventional IC processing, provided due consideration is given to the thickness and character of the masking resist layer. The plasma etching of oxide layers with adequate selectivity can now be achieved and is particularly useful for the high resolution etching of windows in phosphorous-doped oxide layers.